In the immediate future, clean water availability will become a more important issue than the availability of oil. Estimates have been made that in only twenty years China will only have enough clean water for 20% of its population. Every aspect of society has a cost that is directly related to clean water. An effective means to clean waterways is required. This need is urgent, and the cost of taking action escalates every day. The economic interests of communities are seriously impacted by this need. It is not uncommon for industries to employ water experts to evaluate future alternative sites based on the quality and quantity of water.
Evapotranspiration
Solar heating is the energy input from the sun that drives the hydrologic cycle (sometimes referred to as “evapotranspiration”) by evaporating water from oceans and rivers and depositing precipitation on land as rain and snow. FIG. 1 presents an illustrative diagram of the cycle of evapotranspiration. Evapotranspiration and solar heat are central to all water movement, along with gravity, wind, and the rotation of the earth. With the rotation of the earth, water is moved depending on the hemisphere in a certain direction. In the northern hemisphere, water moves in a counter-clockwise motion, while it moves in a clockwise motion in the southern hemisphere.
All fresh water in the world moves continuously in a closed-loop system. No new water is created. Water from precipitation becomes surface water in lakes and rivers. This surface water seeps into the ground to become groundwater. Groundwater, in turn, also feeds surface water. Water circulates from sky to land to ocean and back again. This is the evapotranspiration closed-loop system. With water movement within evapotranspiration, only so much water is available for human use. Annual discharge of the world's water from land to oceans varies, but 40,000 km3 per year is typical. Only 12,500 km3 of runoff is available for human consumption because the majority of runoff occurs in lightly populated areas or seasonal flood plains. Of this 12,500 km3, about 43% is estimated to already be polluted. This means that although two-thirds of our planet is covered in water, only about 5,375 km3—about 13%—of the world's water is available and suitable for human consumption. As is true for all organisms, large amounts of fresh clean water are necessary for survival of a species.
Stream Characteristics
Stream characteristics effect pollution and clean-up. Water movement and flow, sediment, temperature, oxygen, carbon dioxide, and water chemistry are critical stream characteristics that have to be in complete harmony. Water movement is of three types in a stream. These are: (a) turbulence, which occurs in open water, (b) laminar, which is more common close to solid surfaces or in the pores of sediment and silt, and (c) molecular, which also is termed Brownian motion.
Water flow and discharge in a stream is determined by the formula Q=wdv. Water flow (Q) is equal to the width (w) of the stream multiplied by the depth (d) and velocity (v) of the stream. Stream flow is the amount of water flowing down a stream or river. “Instream flow” is the term that defines the flow levels in a stream necessary to protect the aquatic biota of an individual stream. Instream flow is a specific number measured in cubic feet per second (CFS) for a given stream on a month-by-month basis. This number becomes a water right for a specific stream. This regulatory number can be used by ecologists to determine if a stream has sufficient water for new water use. The flow rate contributes to the beauty of a stream, influences ground water levels, as well as other surface water levels in ponds, lakes, and wetland areas. If the water in the stream is good for fish, then it will be suitable for humans.
Stream studies use either the Instream Flow Incremental Methodology (IFIM) or the Toe-width Method, which uses stream bank measurements to study stream flow, to measure instream flow. After establishing the mean annual flow (MAF) of a stream, the Tennant method can be used for environmental flow assessment of a stream. Riffles in a stream have the highest area of macro-invertebrate production and are the first areas to go dry. This implication from low riffle discharge means low food supply and oxygen for the stream biota. The relationship between discharge and wetted perimeters is estimated often for riffles because of the high concentration of macro-invertebrate production in these areas.
Sediment is naturally-occurring material formed by the processes of weathering or erosion and settles on the banks and the bottom of a body of water. It can be classified into three zones: erosion, transfer, and deposition. Erosion begins at the start of a stream. Transfer occurs in the middle of the stream, and deposition of sediment is found at the end of the stream (e.g. Mississippi Delta). “The supply and transport of sediments in a stream are important because they strongly influence the channel dynamics, affect habitat quality experienced by the biota, and can be extremely costly to manage.” See Allan and Castillo (2009). Sediment is a source of chronic, often dangerous, pollution (e.g. heavy metals) resulting in stream water quality that will be costly for humans as well as affecting the infrastructure of the stream.
Water temperature is expressed in several units (K, Kelvin; ° C., Celsius; ° F., Fahrenheit). The temperature range in a stream for aquatic viability is between 40° F. and 80° F. at the highest. Many invertebrates and vertebrates such as dipteran larvae, midges, brown trout, and other cold water fish cannot live in temperatures above 80° F. The ideal temperature for a healthy stream is 57.5° F. all year round.
Water chemistry is yet another important characteristic affecting clean up. Rain is an acid with a pH near 5.7 because of its carbon dioxide content and naturally occurring sulfate. In addition, humic acid from decaying plant matter caused a decrease in pH rainwater runoff ranging from 4-5. In urban areas, runoff of salts and other de-icing compounds applied to roads can greatly elevate the salinity of receiving waterways, causing large fluctuations in pH.